The present invention provides a process for immobilizing organic and inorganic pollutants in contaminated soil materials of a remediation site.
It is state of the art that swelling clay materials are used for adsorbing heavy metal ions in wastewater treatment systems and that organo-bentonites which have high adsorption properties are used to upgrade landfill barriers.
U.S. Pat. No. 4,473,477 describes a process for the controlled storage of materials containing organic pollutants, which are bonded for adsorption into an organophilic bentonite (organoclay). To this end, an organophilic bentonite is used to bind liquid or solid contaminated organic material. It is of disadvantage that the whole landfill body must be treated with organophilic bentonite, or that leachate is pumped through a filter pad of organophilic bentonite, or that a layer of pure organophilic bentonite be used as landfill sealing. The use of large quantities of organophilic bentonite for this purpose is uneconomical.
Moreover, it is known that barrier material with too high permeability and too small cation exchange capacity or with too little heavy metal adsorption can be improved by adding a swelling clay, e.g. a bentonite treated with S-trimercaptotriazine in the form of sodium salt. This can be done by forced mixing or countersinking or by injection. This permits to achieve quadruple adsorption as compared to a conventional Ca-bentonite. In addition, the swelling effect of the Na-ions becomes effective, causing a substantial reduction of the permeability coefficient which remains constant even after exchanging the heavy metal ions for the Na-ions because the remaining swelling clay materials will exchange these excess Na-ions.
Furthermore, for immobilizing pollutants in soils, bonding processes are known by which the contaminated soil is bonded with e.g. cement. The so consolidated soil is no longer a soil proper but a concrete-like body which cannot be worked any more with the customary foundation engineering equipment, and this has a disadvantageous effect.
When using chemicals for immobilization a frequent disadvantage is their toxicity, and so their handling will cause new contaminations. In case of conventional flushing processes, the pollutants are obtained in diluted form and partly in large quantities because of the long treatment periods. In addition, a conventional flushing is practicable only for the coarse fractions and not for the fine fractions. Apart from that, no immobilization of the remaining pollutants is achieved by means of this flushing method.
It is the task of the present invention to provide a process in which a soil material contaminated with pollutants is treated with a specific addition of clay which causes an immobilization of existing pollutants and/or in which the pollutant content is reduced by flushing.